Tetramisole, or 2,3,5,6-tetrahydro-6-phenylimidazo[2,1-b]thiazole hydrochloride, is used as a veterinary anthelmintic and levamisol of formula (a) given below, that is, the levorotatory isomer of tetramisole, has immunostimulative and immunoregulative activities. ##STR3## Much attention has been paid to these activities for application to immunotherapy for cancer and treatment for autoimmune diseases such as rheumatoid arthritis.
Further, 3-(p-chlorophenyl)-2,3-dihydro-3-hydroxythiazole[3,2-a]benzimidazole-2-ace tic acid (NSC 208828), which has a chemical structure similar to levamisol as shown in formula (b), also has been known to have immunostimulative and carcinostatic activities. Although these activities are ##STR4## lower than in levamisole, its low toxicity has received considerable attention.
Their pharmaceutical effect, toxicity, etc., have yet to be elucidated definitely and thorough investigation has been expected on these compounds and their analogs with similar structure.
The present inventors, in an effort to find compounds having better immunostimulative and immunoregulative activities as compared with these known compounds aforementioned, have synthesized many kinds of novel compounds with basic structures analogous to that of the known compounds mentioned above, studied the pharmaceutical properties, and have come to achieve the present invention.